This invention relates to stabilized thermoplastic polyurethanes, and particularly to stabilized thermoplastic polyurethanes prepared by the condensation-rearrangement reaction between cyclic nitrile compounds and polyols by means of an organotin catalyst.
It is well known that thermoplastic polyurethane compositions are susceptible to thermal degradation when they are exposed to elevated temperatures, resulting in a loss in molecular weight and a reduction in the value of other physical properties of the compositions. Since they are often subjected to high temperatures during post-polymerization processes such as milling and molding it is highly desirable to eliminate or significantly reduce the thermal degradation of these compositions. Many attempts have been made to provide protection against degradation by the addition of various antioxidants, however, the use of conventional stabilizers has been found to be unsatisfactory when the thermoplastic polyurethane is prepared by means of organotin catalysts, especially when the polyurethane is prepared from cyclic nitrile compounds and polyols. Residual organotin compounds remaining in the polyurethane apparently contribute significantly to the thermal instability of the polyurethane.